The present invention relates generally to a method and system for transferring a multiphase flow in a single pipe and, more particularly, to a method and system for parallel pressure boosting of the gas and liquid phases of a multiphase flow. A multiphase flow may include a gas phase, a liquid phase, and a solid phase. For example, pumping for oil may induce a multiphase flow which is comprised of oil, water, and natural gas. In fact, pumping for oil may induce a multiphase flow which is comprised of at least 95 percent natural gas and less than 5 percent oil.
It is important to industry to transfer a multiphase flow to a predetermined location through a single pipe in order to reduce costs. However, the gas phase and the liquid phase of a multiphase flow react differently to the application of pressure. As a result, several different systems have been developed for the transportation of multiphase flows.
One system divides the gas from the liquid and then separately raises the pressures of the gas and the liquid. The gas and the liquid are then transferred in different pipes. However, this system may require relatively high production costs.
French patent numbers 2,424,472 and 2,424,473 teach systems for transferring a two-phase fluid in a single pipe. The systems taught by these patents dissolve or emulsify the free gas in the liquid in order to obtain a more uniform fluid so that the fluid may be processed by the pumping means. However, these systems may require relatively high costs since the incoming flow mixture range may have to be limited, and additional controls are necessary.
Another system uses pumps designed for communicating to multiphase fluids a pressure value that provides for their transfer over a certain distance. However, these pumps are typically adapted for transferring multiphase flows that have a gas-to-liquid ratio within a limited interval. To remedy this limitation, devices are used for controlling the effluents located upstream from the pump in order to deliver a multiphase flow having a desired gas-to-liquid ratio to the pump. However, these devices do not work effectively when there is a sudden variation in the gas-to-liquid ratio.
Yet another system is taught by U.S. Pat. No. 5,377,714. This system utilizes a flow measurement device for separating the gas from the liquid in a multiphase flow.
In light of the shortcomings of known systems, a need exists for a more efficient system for handling a multiphase flow in a single pipe. The present invention provides pressure boosting of a multiphase flow stream. A preferred embodiment of the present invention is particularly useful when the multiphase flow is comprised of at least about 90 to 95 percent gas. However, it should be recognized by those of ordinary skill in the art that the present invention may be utilized when the multiphase flow has a lower percentage of gas.
It is preferred that a system of the present invention permits parallel pressure boosting of gas and multiphase flow by combining a compressor and a multiphase pump system. Because of the synergistic way this combination functions, there are many applications where the present invention may result in substantial reductions in power requirements and installation costs compared to systems using only multiphase pumps for boosting.
A standard pumping system may cover a range from 2,000 to 80,000 BPDe (the combined oil, gas, and water flow rate at inlet conditions). A combination system of the present invention may also cover this range. In fact, it may have a greatly expanded capacity (nearly quintupled).
A preferred embodiment of a system of the present invention divides the incoming flow and pre-conditions the gas flow going to the compressor. The remaining flow may consist of any variation of multiphase flow ranging from 100 percent gas to 100 percent liquids, and it may be managed by the pumping system. A preferred embodiment of a system of the present invention may include a flow strainer, a flow divider, connections to the compressor system, a multiphase pump, and a flow recombiner. It is preferably designed to work with several types of field compressors. A preferred embodiment of a system of the present invention may also include the basic controls, instrumentation, and piping needed for the system to work together.
In addition to the novel features and advantages mentioned above, other objects and advantages of the present invention will be readily apparent from the following descriptions of the drawings and preferred embodiments.